Because the ZF4HP22 gearbox is running at near it's maximum torque handling capacity with the standard diesel, add a re-map or power box and the engine produces more torque than the boxes rated limit. Ergo it will fail sooner with a power box than it would without. Mine went at 104K miles.
What Data is saying make sense, if a transmission system is designed to deal with a maximum torque band then increasing torque through the drive train will mean that eventually something has to give way.
Just off tangent, on the Fiat forum MJ diesel owners have been chipping their engines to increase power. There are now threads about stuffed clutches.
